coastal structures

Document Sample
coastal structures Powered By Docstoc
					 Evaluation of Coastal Area to locate potential sites for Marine Construction Work
                   or review sites of existing Marine Structures


       Monitoring of coastal erosion and accretion using improved resolution Remote
Sensing data can be helpful in change detection of Coastal shoreline. The shoreline
profile undergoes changes in a steady, erratic, momental and long sustaining type. The
Coastal change due to anthropogenic activities has resulted in disturbing the equilibrium
of Coastal environment. The equilibrium imbalance of Coastal areas due to population
concentration are caused by Coastal erosion, Coastal siltation, Pollution and damage to
natural habitat like Mangroves, Coral reefs etc; The disturbance of ecosystem due to
population can be related to Coastal land use pattern and changes in Land use. The use of
high spatial resolution remote sensing data with facility of spectral, synoptic and near real
time data availability has helped in monitoring shoreline changes and monitoring Coastal
Geomorphology. The Coastal zone erosion caused by tidal flooding, cyclonic storms,
waves etc; can help in demarcating zones of sea transgression. It is observed that coastal
zones with high tidal variation will erode the coastal dunes more by process of toe
erosion during high tides. The zones of accretion will normally have wide Coastal areas
with HWL and LWL migrated more towards the Sea (3). The main thrust in Coastal
studies is to identify erosion and accretion zones caused by Littoral drift and to relate
shore line changes to parameters like wave height, sand properties, coastal geometry,
depth of water etc;. The 23.5 meter resolution of LISS-III sensor of Indian Remote
Sensing Satellite (IRS-1C) could be effectively used in demarcating Coastal features like
Mangroves, dunes, spits, estuaries, shoals, beach profile, eroding/accretion zones and
migratory nature of bars, spits, streams etc;(2).
       The shore line changes near harbour is particularly dangerous to the structures
both on and offshore due to exposure of foundations due to scouring action and
deposition at the area where shallow water is not permitted(1).A database on Coastal area
can be generated. The database can have linkage between spatial map along with the
relevant attributes information pertaining to Coastal erosion and deposition. The database
can have information from other relevant sources including field investigation. to analyze
the performance potential of coastal changes monitoring and subsequent planning for
locating Marine structures or to evaluate the existing marine structures.

Study Area and methodology

        The Coastal stretch covering surrounds of Mumbai Coastal area has been studied
with IRS-IC, LISS-III data. The coastal erosion and accretion through both natural and
anthropogenic process has been studied by analyzing various coastal features such as
beaches, tidal flats, mangroves,   Morphological changes due to population, significant
changes in landform near the creek mouth and analyzing shoal stabilization/
development, change of spit dimension along with obstruction of littoral transport due to
marine constructional activities in coastal areas. The coastal land use Map was generated
through Image classification procedure to evaluate the coastal changes.     The classified
Map was imported into vector Geographical Information System (GIS) database
containing relevant attribute and analyzed to generate derived maps that can help in
locating erosion and accretion zones due to various factors.

Results and Discussion

       The study indicated that the shoreline configuration has undergone significant
change over the years, the synoptic view from remote sensing IRS-1C data provides a
smooth shore and at certain stretches the coast is irregular. The visual studies on IRS-IC
data reveals significant information regarding coastal morphology, coastal land use
including marine constructions and mangroves.         It is seen that the coast line has
undergone changes due to variation of high and low water lines, coastal geometry, wind
direction and velocity. The erosion and accretion zones have undergone changes. The
migration of eroding sites could be due to change in convergence zones of waves or due
to manmade structures (2). The Land use pattern has undergone significant changes
owing to coastal development. This has also contributed to coastal erosion and change of
coastline. The coastal landscape indicate variable width of tidal flats and variable profile
due to grain size being well graded and variable slope that is more directed towards the
sea. The geomorphologic features are extensive and have dense vegetal cover with
varying surface texture and certain geomorphic features have moderate density of
vegetation, this has stabilized the erosion process to a certain extent. The centrifugal
drainage patterns are well integrated and can help in increase of sediment load and
formation of accretion zones. It is observed that accretion zones are more near
geomorphologic features and settlement areas due to erosion and anthropogenic
activities. The coastline with vast fetch and receiving wind almost normal to the coastline
direction are more erosion prone. In the transitional zones, there are estuaries where
sediment deposition has occurred. The spits have undergone dimensional changes
however shoal formation is not seen. The uplands support shrubs and medium agriculture
that has finer soil with gentle morphology. This can reduce the erosion. The mangroves
are dense and are located on slopes oriented towards the sea. Field checks were
conducted in the area to validate the satellite data observations.
The attribute schema associated with coastal features that are responsible for coastal
changes and location of erosion/accretion zones were evolved to converge towards
generation of derived maps. The derived maps were useful in locating erosion/accretion
zones in GIS environment. Table-I gives the relevant attributes schema taken for GIS


       The outcome of the IRS-1C data analyzed for study of coastal area to locate the
erosion and accretion zones leading to location of       Marine structures has shown that
LISS-III data can give relevant coastal land use and landscape information that is useful
for understanding the fragile coastal eco-system and managing the coastal environment.
The changes in shorelines, land cover and landscapes due to coastal process and
population can be effectively monitored and ecological sensitive area can be segregated.
The Coastal features along with attributes that control erosion/accretion activities can be
analysed through vector GIS for evolving various derived spatial outputs that can be
evaluated in a integrated manner so as to converge on to the areas prone to erosion and

1.      Chaterjee.S and Ghosh.B.N Compendium of papers presented on Remote sensing
        applications at Indo-US Symposium workshop at Mumbai(1996) 6-9Oct pp113-
2.      Jayappa K S and Subramanya,K.R(1989). Beach morphological changes between
        Talapady and Surathkal, Dakshina Kannada, In: Recent Geoscientific studies in
        the Arabian sea off India.Geological Survey of India.Publication.,24:pp299-306.
3.      Manavalan P and Adiga S(1994). Astudy of coastal zones of Karnataka through
        digital analysis of Indian Remote Sensing Satellite data. Paper presented in the
        workshop on satellite Remote sensing for Coastal zone management held at
        Bangalore, pp-27-31.
4.      Manikiam B, Honne Gowda H, Manavalan P, Jayaraman V and Chandrashekar M
        G (1993). Study of sediment dynamics using satellite remote sensing, Advanced
        Space Research Vol.13, No 5, pp.(5) 75-(5) 78, Great Britain.

     TABLE-I: Attributes associated with Coastal features for vector GIS analysis

COASTAL FEATURES                              ATTRIBUTES
Settlements                                   Type, Density, Extent.

Uplands                                       Morphology, Soil type, Vegetation cover,
                                              Scrub presence.

Transitional zone/wetlands                    Presence of estuary, Presence of Spits,
                       Shoal formation.

Mangroves              Density, Dissected slope and aspect,
                       Ground orientation towards coast.

Geomorphologic Hills   Extent, surface texture, Vegetal cover, Soil
                       type, Soil condition.

Tidal Flats            Width, Profile, Grain size, Slope

Shared By:
Tags: coastal, study